Optical communication systems provide an important way for transferring large amounts of data and other signals at high speeds. An important component in these optical communication systems is an optical transceiver. On the transmission side, the optical transceiver functions to translate an electrical signal representing an information signal (e.g., a digital information signal in the form of 1s and 0s) into an optical signal suitable for transmission via a transmission medium (e.g., an optical fiber). On the reception side, the optical transceiver converts the received optical signal back into an electrical signal that represents the original information signal. An important component in the optical transceiver design is the transmitter for transmitting the optical signal. Typically, the transmitter incorporates a light emitting diode (LED) for transmission rates of the order of megabits/second and a semiconductor laser diode for transmission rates of the order of gigabits/second.
High Speed Design Considerations
As the demand for bandwidth in optical communication systems ever increases, new design considerations and mechanisms are required to achieve higher transmission speeds. Wavelength division multiplexing (WDM) has provided an increased bandwidth through optical fiber. Wavelength division multiplexing (WDM) sends many high-speed optical signals at different wavelengths through the same optical fiber to increase the total bandwidth of the system. Since only a finite portion of the spectral bandwidth of current optical fiber can be used to transmit optical signals, the bandwidth required for each channel limits the number of channels that can be supported by a WDM system.
Current wavelength division multiplexing (WDM) systems are based on two main approaches. One approach uses laser sources that are not temperature controlled. An example of this approach is described by Lemoff, B. E.; Buckman, L. A.; Schmit, A. J.; Dolfi, D. W in A Compact, Low-Cost WDM Transceiver For The LAN, PROCEEDINGS 50TH ELECTRONIC COMPONENTS AND TECHNOLOGY CONFERENCE, 711–716 (2000). However, in this first approach each channel generally requires about 15 nm of bandwidth. A large bandwidth is required since each channel must be able to accommodate optical signals that have a wavelength that depends generally on the temperature of the laser source. As can be appreciated, the number of channels that can be employed in a WDM system is reduced as the bandwidth for each channel is increased.
A second approach utilizes temperature-controlled laser sources. An example of this approach is described in U.S. Pat. No. 4,993,032 entitled, Monolithic Temperature Stabilized Optical Tuning Circuit For Channel Separation In WDM Systems Utilizing Tunable Lasers. Using temperature-controlled laser sources reduces the bandwidth requirements for each channel to a few nanometers. Since the temperature of the laser source is well controlled in these systems, the bandwidth required for each channel is significantly less than the first approach. Consequently, the number of channels that can be supported in these systems is greater than the first approach. These systems are commonly referred to as “dense” WDM (DWDM) systems. Unfortunately, using temperature-controlled laser sources increases the complexity of the transmitter and is expensive to implement.
Accordingly, there is a tradeoff in prior art systems between the number of channels that are supported by a system and the cost of the system attributed to temperature control of the laser.
The prior art approaches do not provide any mechanisms that allow the channel spacing of WDM systems to be reduced without the use of temperature-controlled laser sources. Consequently, what is needed is a WDM receiver that would allow the channel spacing of WDM systems to be reduced without the requiring the use of temperature-controlled laser sources in the transmitter.